1. Field of the Invention
This invention relates generally to the separation of wire-insulating material from its wire, and more particularly, to a method and apparatus for freezing random-size masses and pieces of insulated wire in a shaftless rotatable drum and thereafter grinding the same to produce small-size particles to be separated.
2. Description of the Prior Art
The desirablity of recovering metal and insulation materials from scrap and otherwise discarded conductor wire is well-known. The value of copper which can be recycled is the prime reason for performing such recovery operation. Recovery of other metals such as aluminum, brass and iron also is desirable. The insulation materials on such wire also have value when recovered for use as pulverized filler for packaging and other uses.
Various methods and apparatus are known for performing the recovery operation. In one process, the wire with insulation thereon is burned to eliminate the insulation. The burning method has disadvantages in that it creates impurities from the insulation which contaminate the metal, it makes recovery of the insulation impossible, and most importantly, it results in generation of highly toxic gases which heretofore have been released into the atmosphere with resultant pollution. In an effort to prevent atmospheric pollution, water scrubber devices have been used to eliminate the toxic gases before they are released, but this procedure results in pollution of the water with equal disadvantage. Current environmental protection laws render the burning method not only undesirable, but for the most part illegal.
Another method used heretofore to effect recovery of conductor metal and insulation is to grind or pulverize scrap pieces of wire by use of mills, crushers, rollers and the like. This method obviates the pollution problems attendant with burning processes, but results in other disadvantages. Conductor wire, such as copper, is very malleable at ambient termperature. Large masses, lengths or pieces of such wire tend to jam grinding mills because they are not readily broken-up. When grinding processes per se are used, therefore, the wire to be treated must usually first be reduced to small size pieces or lengths in effort to minimize such jamming of the grinding apparatus. Large masses, lengths, and coils of wire generally cannot be processed in grinding mills until they are first straightened and passed through chopping devices to reduce the same to small lengths or pieces and thereafter ground. These operations use substantial amounts of energy, are time-consuming and often are not successful in preventing jamming of the grinding apparatus.
Attempts have been made to use cryogenic materials such as liquids and gases during treatment of the wire to be separated from its insulation by exposing the wire to the cryogenic material during or immediately prior to the grinding operation. When super cooled, the wire and insulation is rendered brittle. The brittle wire presents much less resistance to a grinding apparatus than wire at ambient temperatures; consequently, the grinding is accomplished faster, with less energy consumption, and with reduced jamming effect on the grinding apparatus.
Prior art structures incorporate the use of conveyors onto which wire scraps and bundles are placed and passed through a cooling unit where the wire is exposed to a cryogenic chemical to freeze the same. The frozen wire passes out of the cooling unit to a grinding or crushing station where grinding and separation of the insulation from the wire is effected. Such processes are disclosed in U.S. Pat. Nos. 3,527,414, 3,647,149 and 3,666,185. To be effective, freezing of the conductor wire masses and pieces must be complete, i.e., all surfaces and internal areas of the wire must be totally frozen. Where conveyor systems such as those disclosed in the aforementioned patents are used, the freezing operation may not result in total penetration of the wire to be treated because the coolant may not reach all surfaces of the wire, such as the undersides thereof resting on the conveyor. It is possible to ensure total freezing of the wire by increasing the time the same is conveyed through the coolant, i.e., by using an extra long conveyor, but such systems would be impractical because of space limitations.
The desired freezing of wire to be ground and separated from its insulating ideally is performed in a rotatable drum into which masses of wire in any volume, size or shape can be placed and exposed to cryogenic material. A drum in which the wire is introduced will continually turn the same for exposure of all surfaces and areas to the coolant. Consequently, total freezing as desired can be accomplished with certainty and in a relatively limited space area. Furthermore, because coolant introduced into a rotating drum will continually contact the wire to be frozen, the amount of coolant required for total freezing will be less than that needed when conveying systems are used.
Presently existing drum designs and constructions do not permit exposure therein of articles to cryogenic materials for several reasons. In the case of a typical drum rotatably mounted on a central shaft with one or more paddle wheels on the interior of the drum to effect simultaneous tumbling and movement of articles therethrough, the pieces of wire to be treated must first be reduced to small lengths because large pieces tend to wrap around the shaft and paddles as they are being agitated. The problem is compounded when the wire is frozen because it then becomes exceedingly difficult to free the frozen wire from the drum to unclog the same. Furthermore, the cryogenic material used, which typically is nitrogen in a liquid atomized state at very low temperatures around -50.degree. C, causes the drum to freeze also and therefore contract since the drum is formed of metal. The contraction of metal when exposed to cryogenic materials and resultant extremely low temperature can be drastic and will have a serious effect on the mechanical operating characteristics of the drum and its drive mechanism. Metal-on-metal parts will freeze making use of the cryogenic material impractical as well as undesirable.